This invention concerns a method for producing a dual porosity body and specifically a method for producing a dual porosity gas electrode by depositing a solid material onto only a portion of the walls of a substrate which has a plurality of interconnected passageways traversing the substrate.
Electrodes suitable for electrochemically reacting a gas with a liquid and having a plurality of interconnected passageways traversing the electrode member are well known in the art. Single porosity electrodes are those in which the diameter of the passageways traversing the member do not vary to a substantial degree. Dual porosity electrodes are known in the art and are described in, for example, U.S. Pat. Nos. 4,341,606 and 4,260,469. Dual porosity electrodes are comprised of two, interconnected, porous layers having passageways which differ in diameter from each other. For electrochemical processes, the passageways in a coarse layer usually have diameters of from about 6 to about 12 microns, while the passageways of a fine layer usually have diameters of from about 0.1 to about 5 microns.
Dual porosity electrodes may be prepared in a variety of ways. Commonly, the coarse and fine layers are prepared separately by bonding or sintering together a plurality of particles. The individual layers are then bonded or sintered to each other. An optional preparation method involves forming one layer by bonding or sintering a plurality of particles together, followed by depositing a slurry of metal powder onto the prepared layer and sintering the layers together. However, in any of these preparation methods, sintering conditions (time and temperature) must be carefully controlled to prevent excessive deformation of the individual layers.
A convenient method to prepare dual porosity electrodes without the problems discussed above would be highly useful. The present invention provides such a method.